Technical Field
The present invention is related to a drive circuit for driving a drive element using a three-value signal. In particular, the present invention can be suitably used for a digital sound system an application of the digital sound system, in which a digital speaker apparatus directly converting a digital signal into analog sound and a drive circuit for driving the digital speaker using a three-value signal are used.
Description of Related Art
WO2007/135928A1 is proposed as a digital-analog conversion device which directly converts a digital signal into analog audio. A system for directly converting a digital signal into analog sound using a circuit which is input with a digital sound signal and outputs a plurality of digital signals and a plurality of coils (unit) which are driven by the plurality digital signals is referred to below as a digital sound system as proposed in WO2007/135928A1.
Such a digital sound system can output a large sound pressure at a low voltage compared to an analog sound system which uses a conventional single speaker or single drive since it uses a plurality of speakers or a plurality of drive units (coils etc), in addition to features such as low system power consumption compared to an analog sound system which drives a speaker using an analog electrical signal.
The digital sound system proposed in WO2007/135928A1 is comprised from a circuit which outputs a plurality of digital signals using a ΔΣ modulator and a mismatch shaping filter circuit, and a digital speaker device which directly converts analog sound by driving a plurality of coils (unit) which are driven by the plurality of digital signals.
FIG. 1 shows a conventional example of a digital speaker device comprised from a circuit which outputs a plurality of digital signals using a ΔΣ modulator and a post-filter circuit, and a plurality of speaker driving elements. A 1 bit digital input signal (101) is input to a ΔΣ modulator (102) and is converted to a plurality of digital signals (103) having n bits by the ΔΣ modulator (102). The plurality of digital signals having n bits are converted to a thermometer code (105) having m bits by a formatter circuit (104) and, following this, are converted to k number of digital signals (107), which are mismatch shaped by the post-filter (106). S number of speaker drive circuits (108) are controlled by the three values of 0, +1, and −1 in response to a digital selection signal.
A conventional example of a drive circuit which drives a driving element using the three values of 0, +1, and −1 in response to a digital selection signal is shown in Japanese Patent Laid Open 2010-028783.
In the digital sound system proposed in WO2007/135928A1, the post-filter removes a noise caused by manufacturing variation of a plurality of coils, the noise being a problem when driving a plurality of coils (units), by using a mismatch shaping method.
As described above, it is demanded that a digital sound system is drives a driving element using the three values of 0, +1, and −1 in response to a digital selection signal. While it is possible to remove the characteristic variation of each of a plurality of driving elements by a mismatch shaping method using a post-filter in the same manner as manufacturing variation between coils (units), there is a problem whereby a noise caused by variation that depends on the transition direction of a driving element which drives a signal with the three values of 0, +1, and −1 cannot be removed.